Methods and computed tomography units are generally known from cardio CT. Reference may be made, for example, to the document by Thomas Flohr and Bernd Ohnesorge entitled “Heart-Rate Adaptive Optimization of Spatial and Temporal Resolution for ECG-Gated Multislice Spiral CT of the Heart”, Journal of Computer Assisted Tomography, 25(6): 907-923. In this known method of CT cardiac imaging an ECG of the patient is recorded in parallel with the CT scan and is stored jointly with the acquired detector data. Detector data that are to be assigned to a specific cardiac phase can then be selected retrospectively with the aid of a typical ECG structure, for example an R wave, and a reconstruction of the image data can be carried out starting with a specific instant of the cycle relative to the R wave. This phase-resolved imaging of the cardiac volume is used both for coronary CT angiography and for functional diagnostics on the heart.
A multiplicity of images that show the overall cardiac cycle at different time intervals are required for functional diagnostics. Accordingly, volume data records are reconstructed at different initial instants relative to the subsequent R wave, the detector data used for the purpose extending, however, over a relatively large cardiac phase period. As a rule, even the data collection periods from which the individual temporally consecutive images are reconstructed overlap one another, because the temporal spacing at which the operator requires consecutive images of the heart is mostly smaller than the period from which the data for the reconstruction of the images must be collected.
Thus, at specific instants of the cardiac phase data records flow repeatedly into the reconstruction of volume data records of different initial instants, the result being a very large calculation volume.